ACIS error 30001:

When I am trying to subtract the volume of runner blades (of Francis turbine)from the volume of water, GAMBIT shows ERROR: ACIS error 30001: coincident face-face-ints with different body vertices. Restoring the geometric model to the state before the current operation (if there is a positive number of default UNDO levels)

How to solve this problem? Also, please let me know from where to refer about ACIS errors.